In the refining of petroleum materials such as crude oil the oil or portions thereof is subjected to a number of processes, both physical and chemical, designed to improve the economic quality of the material. Such processes often include use of processing systems in which the temperature and/or pressure is varied. In one embodiment, distillation procedures are employed to separate the oil or components thereof into fractions of varying structure based on differences in volatility as reflected in differences in boiling points. In other refining operations, the chemical structure of the petroleum materials is altered by conventional procedures such as thermal cracking or hydroprocessing.
In a number of these physical or chemical transformations, hydrogen chloride and ammonia are present or are produced. As a result, it is not uncommon to observe formation and subsequent deposition of ammonium chloride within the processing system. Ammonium chloride is a solid with a sublimation temperature of 340.degree. C. (644.degree. F.) which, upon deposition during processing, can and does foul and plug processing equipment.
In distillation columns employed for physical separations of petroleum material components, when ammonium chloride is present the deposits tend to form on distillation trays, in recycle circuits and in the overheads of the distillation tower, and the resulting deposits cause substantial operating difficulties when the trays or lines become plugged. It is known to remove such deposits by chemical procedures but such methods often result in the undesirable introduction of ammonium chloride into one or more product streams, e.g., into the kerosine or gas oil products.
In operation such as hydroprocessing, the presence of ammonia and hydrogen chloride in the initial feed or the formation thereof during the hydroprocessing also leads to fouling or plugging upon ammonium chloride formation and deposition, frequently in heat exchangers. The conventional method of combatting such deposition is to introduce water at a point upstream of the location where deposition takes place. However, this procedure is not effective if the deposition occurs at a point where water cannot be provided or at a temperature and pressure at which the conventional liquid water wash cannot be applied.
It would be of advantage, therefore, to have an improved method of retarding or preventing ammonium chloride deposition, at least in portions of the petroleum material processing operations where conventional methods cannot be used.